When I click this link it opens up the file in Xcode. Unfortunately there doesn't seem to be any way to change this. I would like it to open in Sublime or Atom. I've checked the GitHub for Mac preferences menu but there is nothing there related to your default editor. I've tried changing my default git editor but that doesn't work either. How do I set the editor GitHub for Mac uses?
I figured it out. Github for Mac uses the same application that finder would use if you double clicked on the file. You can follow these instructions to change the default application for a given file type http://computers.tutsplus.com/tutorials/quick-tip-how-to-change-the-default-application-to-open-files--mac-51413.